Time-dependent effects of fructose on the modulation of a reactivated memory

1. A passive-avoidance-to-active-avoidance negative transfer paradigm was used to investigate systematically the time-dependent effects of fructose on reactivated memories in rats. 2. Memory reactivation consisted of re-exposing the rats 24 hr after passive-avoidance conditioning to environmental and learning cues present during training; post-reactivation injections of fructose (100 mg/kg, sc) or saline were followed 24 hr later by active-avoidance (discrimination reversal) conditioning. Fructose or saline was administered in the experimental room 0, 2, 5, or 30 min, or in the colony room 60 min, after reactivation. 3. The results showed a time-dependent decrease in the ability of fructose to modulate a reactivated memory. 4. These results suggest that the time-dependent effects for the modulation of a reactivated memory by fructose (a hexose that does not readily pass the blood-brain barrier) and glucose (a hexose that readily passes the blood-brain barrier) follow similar trends.